Now to get serious. Really, really serious. Not to imply those Boys of Summer weren’t before, but for teams in contention for the playoffs, September brings heightened pressure and significance.

The Dodgers are definitely in contention, definitely primed for a stretch run, if a tad less comfortably than it seemed a few days ago when they were up by five games.

Now, as they prepare Monday for the final month by hosting the playoff-bound Washington Nationals for three games, their division lead has been cut to 2 1/2 by the Giants with 25 games left to play.

Its big-boy time.

The Dodgers began the fortifying of their roster Monday, the first day it could be expanded, by calling up four players, including the highly touted outfielder Joc Pederson and hot Cuban prospect Alex Guerrero.

Because this is earn-the-paycheck time, when the importance of games is magnified, when it’s time to win every day. A fact hardly lost on Dodgers management.

“Right now we’re not looking to try people out, looking to get guys extra at-bats, trying to be fair to anybody,” Manager Don Mattingly said. “We’re trying to win games.”

As long as the Dodgers are playing to win a playoff spot, neither Pederson, Guerrero nor the other two called up Monday -- catcher Tim Federowicz and right-hander Yimi Garcia -- are expected to make any kind of major contribution.

The Dodgers will try to win the National League West with the team that catcher A.J. Ellis previously said has been kind of “plodding along” this season. Pederson and Guerrero will mostly be seen as pinch-hitters.

“We’re in a pennant race,” Mattingly said. “We’re not just trying guys out and giving shots at places.”

Players called up from Sept. 1 on are not eligible for the postseason roster. The only way they can be added is if they are replacing an injured player at the same position.

The Dodgers also activated Chris Perez from the disabled list Monday, and are expected to bring back right-hander Carlos Frias and infielder Miguel Rojas on Tuesday after the minor league season ends Monday. Frias is expected to make a spot start Wednesday.

Later, if Paco Rodriguez proves healthy, he and others could be added.

But the Dodgers dug in with the team they’ve primarily had all year when the trading deadline passed without their adding a significant player.

Time for them to step up, to win this thing or not.

“For me, this is the exciting time of year,” Mattingly said. “Everybody loves seeing great players in pressure situations down the stretch.

“This is going to be an exciting time for us, as a Dodger fan and for me as a manager, just to watch our guys. We’ve got Hanley Ramirez, Matt Kemp, Adrian Gonzalez. On and on, right? And I think it’s going to be fun to see how they step their game up.”